Silymarin is a plant extract extracted from fruits and seeds of a medicinal plant, Silybum marianum (L.) Gaertn. of Family Compositae, wherein the main ingredients are flavonoids such as silybin, isosilybin, silydianin, silychristin, etc. Silymarin has functions of protecting liver, anti-oxidation, reducing blood fat, clearing away heat and toxic materials, soothing liver-gallbladder, and the like. The main specifications of the silymarin product in market comprise: the total content of silymarin (UV)≧80%, wherein the content of silybin and isosilybin, i.e., double silybins content (HPLC)≧30%; and the total content of silymarin (UV)≧80%, wherein the content of silybin, i.e., single silybin content (HPLC)≧30%.
There are a lot of industrial production methods of silymarin reported currently. In the extraction process of silymarin, the solvent for extraction is mainly ethyl acetate, acetone, methanol, ethanol, alkaline water or a mixed solution of ethanol and alkaline water, or the like. When extraction is carried out with a solvent such as methanol, ethanol, alkaline water or a mixed solution of ethanol and alkaline water, or the like, the extract would contain many impurities (mainly high polar impurities, such as carbohydrates, proteins and others); further, after dried, the crude extract also needs to be extracted with other solvents (such as acetone, ethyl acetate, etc.) or purified by other processes (such as, purified by macroporous resin, silica gel, etc.), so that the product may meet quality requirements. By extraction with ethyl acetate, the water in the cake residue of the raw material Silybum marianum and the extraction system would go into ethyl acetate continuously, causing reverse reaction, so that ethanol and acetic acid are produced; meanwhile, the solvent polarity and solubility are changed, so that the quality and the yield of the product are decreased. The results obtained with acetone extraction are more desirable, but extraction with a single solvent acetone would result in a long extraction time (a extraction time up to 8 hours or more) and low efficiency.
The separation and purification of silymarin are performed primarily by crystallization, macroporous resin, or silica gel, or the like. The purity of the product obtained by these treatments is relatively higher, but the process is complex, the processing time is long, and the cost is relatively higher. Furthermore, since Silybum marianum seed oil is not removed thoroughly by pressing Silybum marianum seeds, the residual oil in the pressed Silybum marianum seeds needs to be removed further by degreasing with water, n-hexane or petroleum ether, or the like. The disadvantage of the process lies in that there is still residual oil, reducing the product quality. For example, a process of producing silymarin by acetone is disclosed in Chinese Patent Application No. CN01101489.X (publication No. CN1317486A, publication date: Oct. 17, 2001). In this process, the raw material is pressed to obtain oil, which is extracted with acetone; the extract is concentrated to give a Silybum marianum seed ointment; the Silybum marianum seed ointment is dried before it is degreased with petroleum ether; the degreased Silybum marianum seed ointment is dried again to give a silymarin product. An extraction method of silymarin with less soluble residues and high content is disclosed in Chinese Patent Application No. CN201010600010.0 (publication No. CN102558162A, publication date: Jul. 11, 2012). The pressed Silybum marianum seed cake is used as a raw material, and extracted with acetone; the obtained extract is concentrated to give a pasty extractum; water is added to the pasty extractum to wash away soluble residues and residual oil, and the obtained mixture is dried to give a silymarin product. In both of two processes above, the process of removing residual oil is washing away the oil in the ointment or the extractum, thereby there exists a problem that the residual oil is not removed thoroughly, resulting in a product with poor quality.
Therefore, it is necessary to provide a method for producing silymarin, which can greatly improve the extraction efficiency and yield, shorten the extraction time; have a simple process and low cost, remove the residual oil thoroughly, and produce products with low impurities and high quality and purity, and thus which has a great application prospect and an economic value in industrial production.